Dasatinib combined with docetaxel for castration-resistant prostate cancer: Results from a phase 1-2 study

BACKGROUND: To determine the potential efficacy of targeting both the tumor and bone microenvironment in patients with castration-resistant prostate cancer (PC), the authors conducted a phase 1-2 trial combining docetaxel with dasatinib, an oral SRC inhibitor. METHODS: In phase 1, 16 men received dasatinib 50 to 120 mg once daily and docetaxel 60 to 75 mg/m ² every 21 days. In phase 2, 30 additional men received dasatinib 100 mg once daily/docetaxel 75 mg/m ² every 21 days. Efficacy endpoints included changes in prostate-specific antigen (PSA), measurable disease, bone scans, and markers of bone metabolism. Safety and pharmacokinetics were also studied. RESULTS: Combination dasatinib and docetaxel therapy was generally well tolerated. Thirteen of 46 patients (28%) had a grade 3-4 toxicity. Drug-drug interactions and a maximum tolerated dose were not identified. Durable 50% PSA declines occurred in 26 of 46 patients (57%). Of 30 patients with measurable disease, 18 (60%) had a partial response. Fourteen patients (30%) had disappearance of a lesion on bone scan. In bone marker assessments, 33 of 38 (87%) and 26 of 34 (76%) had decreases in urinary N-telopeptide or bone-specific alkaline phosphatase levels, respectively. Twenty-eight patients (61%) received single-agent dasatinib after docetaxel discontinuation and had stabilization of disease for an additional 1 to 12 months. CONCLUSIONS: The high objective response rate and favorable toxicity profile are promising and justify randomized studies of docetaxel and dasatinib in castration-resistant PC. Parallel declines in levels of PSA and bone markers are consistent with cotargeting of epithelial and bone compartments of the cancer. Treatment with single-agent dasatinib following docetaxel cessation warrants further study.